This means that one should expect (at least) two sets of QNMs for Exotic compact objects (ECOs) or fuzz-balls. For massive probes there might be (innermost) stable circular orbits (ISCO) where light particles can be trapped and emit electro-magnetic radiation that 'pollutes' (in that it represent an environmental effect) the photon-sphere and other features of the BH in vacuo [1]}, [2]}, [3]}, [4]}.
